System and method for LED packaging
System and method for LED packaging. The present invention is directed to optical devices. More specifically, embodiments of the presentation provide LED packaging having one or more reflector surfaces. In certain embodiments, the present invention provides LED packages that include thermal pad structures for dissipating heat generated by LED devices. In particular, thermal pad structures with large surface areas are used to allow heat to transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations. There are other embodiments as well.
Latest Soraa, Inc. Patents:
This application is a divisional application of U.S. patent application Ser. No. 12/879,784, filed on Sep. 10, 2010, which claims priority from U.S. Provisional Patent Application No. 61/241,459, filed on Sep. 11, 2009; U.S. Provisional Patent Application No. 61/241,457, filed on Sep. 11, 2009; and U.S. Provisional Patent Application No. 61/241,455, filed on Sep. 11, 2009, commonly assigned and incorporated by reference herein for all purposes.
BACKGROUND OF THE INVENTIONThis invention is directed to optical devices. More specifically, embodiments of the invention provide LED packaging having reflector surfaces, and in some implementations provide LED packages that include thermal pad structures for dissipating heat generated by the LED devices. In particular, thermal pad structures with large surface areas are used to provide heat transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations.
In the late 1800's, Thomas Edison invented the light bulb. The conventional light bulb, commonly called the “Edison bulb,” has been used for over one hundred years. The conventional light bulb uses a tungsten filament enclosed in a glass bulb sealed in a base, which is screwed into a socket. The socket is coupled to an AC power or DC power source. The conventional light bulb can be found commonly in houses, buildings, and outdoor lightings, and other areas requiring light. Unfortunately, the conventional Edison light bulb dissipates much thermal energy. More than 90% of the energy used for the conventional light bulb dissipates as thermal energy. Additionally, the conventional light bulb eventually fails due to evaporation of the tungsten filament.
Fluorescent lighting overcomes some of the drawbacks of the conventional light bulb. Fluorescent lighting uses an optically clear tube structure filled with a noble gas, and typically also contains mercury. A pair of electrodes is coupled between the gas and to an alternating power source through a ballast. Once the mercury has been excited, it discharges to emit UV light. Typically, the optically clear tube is coated with phosphors, which are excited by the UV light to provide white light. Many buildings use fluorescent lighting and, more recently, fluorescent lighting has been fitted onto a base structure, which couples into a standard socket for household use.
Solid state lighting techniques have also been developed. Solid state lighting relies upon semiconductor materials to produce light emitting diodes, commonly called LEDs. At first, red LEDs were demonstrated and introduced into commerce. Modern red LEDs use Aluminum Indium Gallium Phosphide or AlInGaP semiconductor materials. Most recently, Shuji Nakamura pioneered the use of InGaN materials to produce LEDs emitting light in the blue color range for blue LEDs. The blue LEDs led to innovations such as solid state white lighting, the blue laser diode, which in turn enabled the Blu-Ray™ DVD player (trademark of the Blu-Ray Disc Association), and other developments. Blue, violet, or ultraviolet-emitting devices based on InGaN are used in conjunction with phosphors to provide white LEDs. Other colored LEDs have also been proposed.
To take advantage of LED devices, well designed LED packages that house LED devices and provide electrical connections are essential. Numerous types of conventional LED packages have been used, however, they suffer from various disadvantages.
BRIEF SUMMARY OF THE INVENTIONThis invention is directed to optical devices. More specifically, embodiments of the invention provide LED packaging having reflector surfaces, and in some implementations provide LED packages that include thermal pad structures for dissipating heat generated by the LED devices. In particular, thermal pad structures with large surface areas are used to provide heat transfer. In certain embodiments, thick thermally conductive material is used to improve overall thermal conductivity of an LED package, thereby allowing heat generated by LED devices to dissipate quickly. Depending on the application, thermal pad structure, thick thermal conductive layer, and reflective surface may be individually adapted in LED packages or used in combinations.
In one embodiment, this invention provides an optical device with a substrate and an interior surface. The device also includes a conductive layer having a thickness of at least 15 um overlying a portion of the surface. The optical device further includes an LED electrically coupled to the conductive layer, and a layer of insulating material overlaying the interior surface. A reflective layer overlies the insulating material, and preferably has a reflectivity of at least 95%.
According to another embodiment, the invention provides an optical device which includes a substrate with a flat surface. A first conductive region overlies a first portion of the flat surface, and a separate second conductive region overlies a second portion of the flat surface. The optical device includes a first via structure on the first conductive region, and an electrically separated second via structure on the second conductive region. The device additionally includes a thermal pad structure overlaying a third portion of the flat surface. The thermal pad structure is electrically insulated from the first conductive region and the second conductive region. The third portion preferably covers at least 50% of flat surface.
According to another embodiment, the invention provides an optical device. The device includes a substrate with an interior surface and a bottom side. A top conductive layer, preferably having a thickness of at least 15 um overlies a portion of the interface surface. A bottom conductive layer overlies a portion of the bottom side of the substrate. An LED is electrically coupled to a location of the top conductive layer, and a reflective layer overlies the top conductive layer. The reflective layer preferably has a reflectivity of at least 95%.
The device and method of manufacture provide for improved lighting with improved efficiency. They are easier to manufacture using conventional technologies. In certain embodiments, thermal management structures are able to greatly improve thermal conductivity of the LED package. In a specific instance, thermally conductive material as a part of the conductive layer can improve thermal conductivity by almost 50%. For example, the thermal conductivity of a conventional LED package is about 13° C./W. By increasing the thickness of conductive layers according to an embodiment of the present invention (e.g., 50 microns of copper material illustrated in
A further understanding of the nature and advantages of the present invention may be realized by reference to following portions of the specification and attached drawings
As explained above, LED chips are often used as a light source. For LED chips to function, they are secured into a package and electrically coupled to an energy source. The optical efficiency of an LED package is related the reflectivity of the cavity surfaces.
According to an embodiment, the invention provides an improved reflector.
It is to be appreciated that embodiments of the present invention provides other ways to enhance reflectivity, thereby improving overall LED package performance. In certain embodiments, reflectivity of an LED package is enhanced by increasing the coverage of reflective areas.
In certain embodiments, the present invention provides thermal management means for the LED packages. More specifically, thermal management pads are provided for surface mount LED packages. For surface mount LED packages, the mounting surfaces typically have three contacts: two electrical contacts and an electrically isolated thermal contact. For example, an LED device is mounted onto a circuit board (such as a metal clad PCB) with matching contact pads. In operation, the LED device often generates a large of heat that needs to be dissipated, as the heat might cause problem even device break down.
In an embodiment, the heat generated by the LED package is conducted across one or more thermal pad structures. More specifically, the thermal pad structures with relatively large surface area are positioned in proximity of the electrical contacts. In principle, the area of the thermal pad directly affects the contact resistance. For example, a larger the thermal pad area translates a lower the thermal resistance, as heat can dissipate through the large area.
In an LED package that is mounted onto a metal clad PCB, the metal clad PCB has a dielectric layer that electrically isolates the electrical circuits from the base metal. For example, the base metal can be aluminum or copper. Unfortunately, the dielectric layer often has a very low thermal resistance of about 2.2° C./W compared to thermal resistance of copper at 400° C./W. As a result, the dielectric layer can be a thermal choke point. In particular for silicon packages where the VIA structures for the electrical contacts are formed by etching silicon substrate material, the VIA location can limit the size of the thermal pad.
It is therefore to be appreciated that embodiments of the present invention provide improved thermal management structures, such as thermal pad structure with large surface area.
It is to be appreciated that the increase thermal pad area greatly increases the rate of heat dissipation by the thermal pad structure.
In comparison, thermal pad structures according to embodiments of the present invention reduces thermal resistance by a substantial amount.
It is to be appreciated that the specific designs of the thermal pad can be varied depending on the application. In certain embodiments, heat dissipation is accomplished by increasing the thickness of thermal conductive material.
Usually, silicon based LED packages are advantageous as they can processed in large wafer scaled formats. For example, up to 8″ silicon wafers are being processed today verses only 2″×4″ ceramic tiles used in the early days. However, the conductivity of silicon (80-140 W/m/k) is relatively low when compared to copper (3090 W/m/k) and other metal materials. Further, in some implementations, the thickness of silicon on which the LED is bonded can be rather thin. Sometimes, the thickness of the silicon material can be as low as 150 um. As a result, the thickness and the thermal conductivity of the silicon material limit the thermal spreading and increase thermal resistance, which is highly undesirable for high power densities applications.
In various embodiments, the present invention provides LED packages with thick conductive layers that help dissipate heat from the LED package.
It is to be appreciated that other variations of thermal management structures are available as well.
LED packages with thermal management structures as shown in
In one or more preferred embodiments, the thermal management structures such as thermal pad and conductive layers can be arranged different or constructed using different types of materials. Similarly, various types of material may be used for the insulating later to improve the reflectivity of the reflective layer. Of course, there can be other variations, modifications, and alternatives. Therefore, the above description and illustrations should not be taken as limiting the scope of the present invention which is defined by the appended claims.
Claims
1. An optical device comprising:
- an electrically insulating substrate defining an opening, the opening having an interior surface;
- a conductive layer overlying a portion of the interior surface, a portion of the conductive layer being characterized by a thickness of at least 15 μm;
- an LED device electrically coupled to the portion of the conductive layer;
- a layer of insulating material overlying the interior surface and the conductive layer; and
- a reflective layer overlying the layer of insulating material, wherein the reflective layer comprises an opening for a bond pad.
2. The device of claim 1 wherein the device is characterized by a thermal resistance of less than 10° C./W.
3. The device of claim 1 wherein a portion of the substrate positioned below the conductive layer is characterized by a thickness of at least 120 μm.
4. The device of claim 1 wherein the reflective layer comprises a metal.
5. The device of claim 1 wherein the insulating material comprises titanium oxide.
6. The device of claim 1 wherein the insulating material comprises silicon oxide.
7. The device of claim 1 comprising a thermal pad coupled to the interior surface.
8. The device of claim 1 wherein the conductive layer is characterized by a thickness of at least 25 μm.
9. The device of claim 1 wherein the insulating material comprises a dielectric material.
10. The device of claim 1 wherein the conductive layer comprises copper.
11. The device of claim 1 wherein the interior surface comprises a flat surface.
12. The device of claim 11 wherein the reflective layer overlies at least a portion of the flat surface.
13. The device of claim 12 wherein the reflective layer comprises a metal.
14. The device of claim 1 comprising a bond pad positioned within the opening defined by the reflective layer.
15. The device of claim 1 wherein the conductive layer comprises a first conductive region and a second conductive region and an insulation region between the first conductive region and the second conductive region, wherein the insulation region comprises titanium oxide.
16. The device of claim 1 wherein the conductive layer comprises a first conductive region and a second conductive region and an insulation region between the first conductive region and the second conductive region, wherein the insulation region comprises silicon oxide.
17. An optical device comprising:
- an electrically insulating substrate having a top side and a bottom side opposing the top side, wherein the top side defines an opening having an interior surface;
- a top conductive layer overlying a portion of the interior surface, a portion of the top conductive layer having a thickness of at least 15 μm;
- a bottom conductive layer overlying and contacting a portion of the bottom side of the substrate;
- an LED device electrically coupled to the top conductive layer; and
- a reflective layer overlying the top conductive layer, wherein the reflective layer comprises an opening for a bond pad.
18. The optical device of claim 17 comprising an insulating layer positioned between the top conductive layer and the reflective layer.
19. The device of claim 17 wherein the device is characterized by a thermal resistance of less than 10° C./W.
20. The device of claim 17 wherein a portion of the substrate positioned below the first conductive region is characterized by a thickness of at least 120 μm.
21. The device of claim 17 comprising an insulating layer overlying at least a portion of the interior surface.
22. The device of claim 21 wherein the insulating layer comprises titanium oxide.
23. The device of claim 17 wherein the interior surface comprises a flat surface.
24. The device of claim 23 wherein the reflective layer overlies at least a portion of the flat surface.
25. The device of claim 17 wherein the reflective layer comprises a metal.
26. The device of claim 17 comprising a bond pad positioned within the opening defined by the reflective layer.
6335771 | January 1, 2002 | Hiraishi |
6498355 | December 24, 2002 | Harrah et al. |
6864641 | March 8, 2005 | Dygert |
6956246 | October 18, 2005 | Epler et al. |
7009199 | March 7, 2006 | Hall |
7083302 | August 1, 2006 | Chen et al. |
7113658 | September 26, 2006 | Ide et al. |
7285799 | October 23, 2007 | Kim et al. |
7560981 | July 14, 2009 | Chao et al. |
7737457 | June 15, 2010 | Kolodin et al. |
7791093 | September 7, 2010 | Basin et al. |
7906793 | March 15, 2011 | Negley |
8044609 | October 25, 2011 | Liu |
8203161 | June 19, 2012 | Simonian et al. |
8269245 | September 18, 2012 | Shum |
8404071 | March 26, 2013 | Cope et al. |
8410711 | April 2, 2013 | Lin et al. |
20010022495 | September 20, 2001 | Salam |
20040190304 | September 30, 2004 | Sugimoto et al. |
20040195598 | October 7, 2004 | Tysoe et al. |
20040227149 | November 18, 2004 | Ibbetson et al. |
20050084218 | April 21, 2005 | Ide et al. |
20050199899 | September 15, 2005 | Lin et al. |
20050224830 | October 13, 2005 | Blonder et al. |
20060006404 | January 12, 2006 | Ibbetson et al. |
20060038542 | February 23, 2006 | Park et al. |
20060068154 | March 30, 2006 | Parce et al. |
20060097385 | May 11, 2006 | Negley |
20060205199 | September 14, 2006 | Baker et al. |
20070018184 | January 25, 2007 | Beeson et al. |
20070114563 | May 24, 2007 | Paek et al. |
20070170450 | July 26, 2007 | Murphy |
20070181895 | August 9, 2007 | Nagai |
20080194054 | August 14, 2008 | Lin et al. |
20080206925 | August 28, 2008 | Chatterjee et al. |
20080210958 | September 4, 2008 | Senda et al. |
20080261341 | October 23, 2008 | Zimmerman et al. |
20090250686 | October 8, 2009 | Sato et al. |
20090252191 | October 8, 2009 | Kubota et al. |
20090309110 | December 17, 2009 | Raring et al. |
20100001300 | January 7, 2010 | Raring et al. |
20100006873 | January 14, 2010 | Raring et al. |
20100148210 | June 17, 2010 | Huang et al. |
20100164403 | July 1, 2010 | Liu |
20110038154 | February 17, 2011 | Chakravarty et al. |
20110068700 | March 24, 2011 | Fan |
20110069490 | March 24, 2011 | Liu |
20110103064 | May 5, 2011 | Coe-Sullivan et al. |
20110108865 | May 12, 2011 | Aldaz et al. |
20110291548 | December 1, 2011 | Nguyen et al. |
20110317397 | December 29, 2011 | Trottier et al. |
20120043552 | February 23, 2012 | David et al. |
20120299492 | November 29, 2012 | Egawa et al. |
20120313541 | December 13, 2012 | Egawa et al. |
20130043799 | February 21, 2013 | Siu et al. |
- Iso et al., ‘High Brightness Blue InGaN/GaN Light Emitting Diode on Nonpolar m-Plane Bulk GaN Substrate,’ Japanese Journal of Applied Physics, 2007, vol. 46, No. 40, pp. L960-L962.
- International Search Report of PCT Application No. PCT/US2011/048499, dated Feb. 14, 2012, 2 pages total.
- Sato et al., ‘Optical Properties of Yellow Light-Emitting Diodes Grown on Semipolar (1122) Bulk GaN Substrate,’ Applied Physics Letters, vol. 92, No. 22, 2008, pp. 221110-1-221110-3.
- USPTO Office Action for U.S. Appl. No. 12/481,543 dated Jun. 27, 2011.
- USPTO Office Action for U.S. Appl. No. 12/491,176 dated Mar. 1, 2012.
- USPTO Office Action for U.S. Appl. No. 12/491,176 dated Jul. 19, 2012.
- USPTO Office Action for U.S. Appl. No. 12/880,889 dated Feb. 27, 2012.
- USPTO Office Action for U.S. Appl. No. 12/880,889 dated Sep. 19, 2012.
- USPTO Office Action for U.S. Appl. No. 12/914,789 dated Oct. 12, 2011.
- USPTO Office Action for U.S. Appl. No. 12/914,789 dated Feb. 24, 2012.
- USPTO Notice of Allowance for U.S. Appl. No. 12/914,789 dated May 17, 2012.
- USPTO Office Action for U.S. Appl. No. 13/019,897 dated Mar. 30, 2012.
- USPTO Office Action for U.S. Appl. No. 13/025,833 dated Jul. 12, 2012.
- USPTO Office Action for U.S. Appl. No. 13/211,145 dated Oct. 17, 2012.
- Csuti et al., ‘Color-matching experiments with RGB-LEDs’, Color Research and Application, vol. 33, No. 2, 2008, pp. 1-9.
- Davis et al., ‘Color Quality Scale’, Optical Engineering 49(3), 2010, pp. 033602-1-16.
- Paper and Board Determination of CIE Whiteness, D65/10 (outdoor daylight), ISO International Standard 11475:2004E (2004), 18 pgs.
- Whitehead et al., ‘A Monte Carlo method for assessing color rendering quality with possible application to color rendering standards’, Color Research and Application, vol. 37, No. 1, Feb. 2012, pp. 13-22.
- USPTO Office Action for U.S. Appl. No. 13/019,897 dated Jan. 16, 2013.
- USPTO Office Action for U.S. Appl. No. 13/210,769 dated Apr. 4, 2013.
- USPTO Notice of Allowance for U.S. Appl. No. 13/298,905 dated Jun. 11, 2013.
Type: Grant
Filed: May 29, 2012
Date of Patent: Mar 18, 2014
Patent Publication Number: 20120235201
Assignee: Soraa, Inc. (Fremont, CA)
Inventor: Frank Tin Chung Shum (Sunnyvale, CA)
Primary Examiner: William D Coleman
Assistant Examiner: John M Parker
Application Number: 13/482,956
International Classification: H01L 33/00 (20100101);